One of the tasks involved in establishing an underwater well is the installation, operation and retrieval of well tools such as tubing hangers, casing hangers, packoff or seal devices, and the like. Other typical tasks include carrying out work-over operations, to service the well. Much work in these areas has been done and it has become common practice to install underwater well components or tools with a handling string, usually in the form of a string of drill pipe, as shown for example in U.S. Pat. No. 4,003,434, issued Jan. 18, 1977, to Garrett et al. Such methods and apparatus have also been applied to multiple string well installations, as seen for example in U.S. Pat. Nos. 3,661,206, issued May 9, 1972, to Putch et al, and U.S. Pat. No. 3,741,294, issued June 26, 1973, to Morrill. While such prior-art efforts have achieved considerable success in the field, there has been a continuing need both for overall improvement and for methods and apparatus which will solve a number of common problems as yet not satisfactorily met. One such problem arises first from the need to maintain communication with well pipes, typically multiple tubing strings, during such operations as landing of a tubing hanger, while providing adequately for blowout protection. That problem becomes more complicated as the water depth increases since, to provide adequate blowout protection conventionally, it is necessary that the tubing strings be positively positioned relative to the blowout preventer, and precise positioning is difficult if not impossible to achieve from the surface by prior-art practices when the strings of pipe extending from the surface to the wellhead are very long. To solve this problem, Kirkland in aforementioned application Ser. No. 36,658 provides a handling string which, while affording communication between the operational base at the surface of the body of water and the well via multiple tubing strings and smaller hydraulic conduits, presents to the blowout preventer a single cylindrical outer surface so that rotational orientation of the handling string relative to the blowout preventer is unnecessary. Though the Kirkland apparatus has proved successful, it has required that at least the lowermost joint of the handling string be built up from a large number of parts, including an outer tubular shell, a plurality of internal pipes and tubes, spacers and partitions, and valve means for filling and emptying the space within the shell. There has accordingly been a need for improvement of apparatus of this type.